shell 語法與C語言對比
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要實現的功能 |
C語言編程 |
Linux Shell腳本編程 |
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程序/腳本的參數傳遞 |
int main(int argc, char** argv) { if (argv != 4) { printf( “Usage: %s arg1 arg2 arg3”, argv[0] ); return 1; }
printf(“arg1:%s/n”,argv[1]); printf(“arg2:%s/n”,argv[2]); printf(“arg3:%s/n”,argv[3]); return 0; } |
#!/bin/sh
if [ $# -lt 3 ]; then echo "Usage: `basename $0` arg1 arg2 arg3" >&2 exit 1 fi
echo "arg1: $1" echo "arg2: $2" echo "arg3: $3" exit 0 |
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int main(int argc, char** argv) { int i; for (i=1; i<=argc;i++) { printf(“arg:%s/n”,argv[i]); } return 0; } |
#!/bin/sh
while [ $# -ne 0 ] do echo "arg: $1" shift done |
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邏輯/數值運算 |
if (d == 0) |
if [ "$D" -eq "0" ] ; then |
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if (d != 0) |
if [ "$D" -ne "0" ] ; then |
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if (d > 0) |
if [ "$D" -gt "0" ] ; then |
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if (d < 0) |
if [ "$D" -lt "0" ] ; then |
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if (d <= 0) |
if [ "$D" -le "0" ] ; then |
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if (d >= 0) |
if [ "$D" -ge "0" ] ; then |
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字符串比較 |
if (strcmp(str,”abc”)==0) { } |
if [ "$STR" != "abc" ]; then fi |
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輸入和輸出 |
scanf(“%d”,&D); |
read D |
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printf( “%d”, D); |
echo –n $D |
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printf( “%d”,D); |
echo $D |
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printf( “Press any to continue...”); char ch=getchar(); printf( “/nyou pressed: %c/n”, ch ); |
#!/bin/sh
getchar() { SAVEDTTY=`stty -g` stty cbreak dd if=/dev/tty bs=1 count=1 2> /dev/null stty -cbreak stty $SAVEDTTY }
echo -n "Press any key to continue..." CH=`getchar` echo "" echo "you pressed: $CH" |
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read D <&3 |
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程序/腳本的控制流程 |
if (isOK) { //1 } else if (isOK2) { //2 } else { //3 } |
if [ isOK ]; then #1 elif [ isOK2 ]; then #2 else #3 fi |
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switch (d) { case 1: printf(“you select 1/n”); break; case 2: case 3: printf(“you select 2 or 3/n”); break; default: printf(“error/n”); break; }; |
case $D in 1) echo "you select 1" ;; 2|3) echo "you select 2 or 3" ;; *) echo "error" ;; esac |
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for (int loop=1; loop<=5;loop++) { printf( “%d”, loop); } |
for loop in 1 2 3 4 5 do echo $loop done |
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do { sleep(5); } while( !isRoot ); |
IS_ROOT=`who | grep root` until [ "$IS_ROOT" ] do sleep 5 done |
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counter=0; while( counter < 5 ) { printf( “%d/n”, counter); counter++; } |
COUNTER=0 while [ $COUNTER -lt 5 ] do echo $COUNTER COUNTER=`expr $COUNTER + 1` done |
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while (1) { } |
while : do done |
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break; |
break或break n，n表示跳出n級循環 |
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continue; |
continue |
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函數與過程的定義 |
void hello() { printf( “hello/n” ); } … //函數調用 hello(); |
hello() { Echo “hello” } 或者 function hello() { Echo “hello” } … #函數調用 hello |
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函數的參數和返回值 |
int ret = doIt(); if (ret == 0) { printf( “OK/n” ); } |
doIt if [ “$?” –eq 0 ] ; then echo “OK” fi 或者 RET = doIt if [ “$RET” –eq “0” ] ; then echo “OK” fi |
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int sum(int a,int b) { return a+b; } int s = sum(1,2); printf(“the sum is: %d/n”, s); |
sum() { echo -n "`expr $1 + $2`" } S=`sum 1 2` echo "the sum is: $S" |
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bool isOK() { return false; } if (isOK) { printf( “YES/n” ); } else { printf( “NO/n” ); } |
isOK() { return 1; } if isOK ; then echo "YES" else echo "NO" fi |
